Caffeine and Carbs

Caffeine and carbohydrates are two of the most reliable performance-boosters out there. So what happens when you combine them? That's what researchers in Taiwan asked in a study just published in the European Journal of Applied Physiology -- and the results were... surprising. They tested the effects of 6 mg per kilogram of body weight of caffeine taken one hour before exercise, and 0.8 g of carbohydrate per kilogram of body weight taken 10 minutes before exercise, using a repeated sprint protocol (10 sets of 5 short 4-second sprints on a stationary bike, with 20 seconds recovery between sprints and 2:00 between sets).

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Here's the peak power they achieved in each set:

Uh oh. There doesn't seem to be any difference, whether you use caffeine alone (CAF+PLA), caffeine and carbohydrate (CAF+CHO), carbohydrate alone (PLA+CHO), or just placebos (PLA+PLA). The same is true looking at other measures like average power and total work done. So what's going on here?

For the carbohydrates, it's pretty simple. Unlike many of the standard carb-and-exercise studies, the 12 subjects were given a standardized meal (500 calories, 65% carb) two hours before the exercise -- so their muscles were already relatively full of carbohydrate. For a marathon, they might still benefit from additional carbs, but for this shorter 60-minute repeated sprint protocol (designed to mimic stop-and-sprint team sports like hockey and basketball), there simply wasn't time for them to run out of carbs. For many athletes, this is a close approximation of real life: in team sports, at least, it's rare that you'd play a game after an overnight fast without eating anything.

This doesn't mean that carbs "don't work." For example, other types of exercise (i.e. sustained efforts like running and cycling) may place greater demands on your carbohydrate stores. But it's a reminder that the big results obtained in lab studies don't always translate to real life conditions. For the most part, in exercise lasting an hour or less, carbs are unlikely to play an important role in your performance if you're not fasting.

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The caffeine results are harder to explain. The authors suggest that it may be a function of the specific protocol of sprints and recoveries, since improvements have been observed with longer sustained efforts as well as with longer recoveries between short sprints. They also found that caffeine seemed to raise cortisol levels when combined with carbohydrate, though those results are a bit hard to interpret. If I had to make a bet, I'd go with the ultra-short sprint protocol as the key variable that caused the lack of response.

One detail I couldn't find mentioned in the study was whether the subjects were habitual caffeine users. They were asked to abstain from caffeine throughout the study period, so if they were coffee addicts, I'd have expected them to get a BIG boost when they were administered caffeine. On the other hand, if they weren't habitual coffee-drinkers, then perhaps the results add more fuel to the suggestion that the apparent performance-boosting effects of caffeine in lab studies are mostly an illusion caused by the withdrawal effect (and consequent performance decline) that occurs when caffeine-addicted subjects are given a placebo instead of caffeine.

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